The objective of this study is to investigate the specific relationship between nocturnal masseter muscle activity, and the signs and symptoms of abnormal jaw muscle function in normal subjects and subjects with myofascial pain. The methods of this project include using a portable cummulative EMG device to establish the average level of masseter muscle activity over a two week period during normal sleep. A measure of the maximum bite force and a measure of the subject's fatigability and his kinesthetic sense will be performed. These measures will be performed on approximately 40 subjects with the absence of any subjective symptoms of jaw dysfunction and in 60 patients who complain of abnormal jaw muscle function but have no TMJ intracapsular dysfunction. An epidemiologic type index will be used to score and evaluate the symptoms of dysfunction along with the occlusal characteristics on all subjects. These subjects will be directed towards establishing levels of nocturnal muscle activity and measures of jaw muscle function in normal and symptomatic subjects. The symptomatic subjects will undergo 6 weeks of treatment either with exercises or an occlusal splint and a followup post-treatment evaluation will be performed on all subjects. In summary, it will be of interest to relate the amount of nocturnal masseter muscle activity to the signs and symptoms of jaw dysfunction. These measures of jaw muscle function will serve as pretreatment records so that any change may be examined for and compared after routine treatment for myofascial pain. This information will hopefully answer the following two questions: 1) "Is there a constant relationship between nocturnal muscle activity, abnormal jaw muscle function and the symptoms of myofascial pain dysfunction, and 2) what effect does occlusal splint therapy vs. exercise-heat therapy have on this relationship, if any.